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Buffer and Ammonia Additions to Corn-Supplemented Native Grass Hay Diets for Beef Heifers^1,2,

Oklahoma Agricultural Experiment Station Stillwater 74078-0425

Abstract

Four mature, ruminally cannulated Hereford x Angus heifers were used to determine the effects of intraruminal dosing of bicarbonate or ammonium compounds on utilization of low-quality grass hay supplemented with corn grain. Isomolar solutions of NaCl (111 g/d), NaHCO₃ (159 g/d), NH₄Cl (102 g/d) or NH₄HCO₃ (150 g/d) were intraruminally dosed 4 times daily. Heifers received 1.75 kg corn supplement once each day plus free-choice native grass hay (4.8% crude protein, 49% acid detergent fiber). Ammonium compounds (NH₄Cl and NH₄HCO₃) increased (P < .05) ruminal NH₃ concentrations. Buffering compounds (NaHCO₃ and NH₄HCO₃) had little effect on ruminal pH. Ruminal pH was .57 units lower (P < .05) with NH₄Cl than with NaCl. Blood pH for NH₄Cl-dosed heifers also was decreased, indicating metabolic acidosis. Buffer alone (NaHCO₃) did not alter utilization or intake of hay, but buffered NH₃ (NH₄HCO₃) increased acid detergent fiber digestibility, hay intake and digestible organic matter intake. Rate of cotton thread disappearance was increased (P < .05) with ammonium compounds (NH4Cl and NH₄HCO₃). Increased particulate (Yb-labeled hay) passage rate was observed only for NH₄HCO₃. Dosing with buffering compounds (NaHCO₃ and NH₄HCO₃) increased (P < .02) ruminal liquid cobalt-ethylenediaminetetra-acetate dilution rate. Inadequate ruminal NH₃ concentrations appear to limit forage digestion when grain supplements are fed. After bacterial N requirements have been met, supplemental buffers could enhance forage utilization if ruminal pH is low.

¹ Journal Article #5222 of the Agric. Exp. Sta., Oklahoma State Univ., Stillwater.

² Authors express appreciation to Dr. Bob Teeter for technical assistance, Stephanie Martin and Les Bourquin for sample collection and laboratory analyses and the Oklahoma State Univ. College of Vet. Med. for surgical preparation of animals.

³ Present address: Texas Agric. Exp. Sta., Overton 75684.

⁴ Reprint requests: Dept. of Anim. Sci., Oklahoma State Univ., Stillwater 74078-0425.